1. Field of the Invention
The present invention relates to a connection structure for a branching connector like a branch pipe, a branch fitting, etc. in a fuel rail such as a high-pressure fuel manifold and a high-pressure fuel block, and more particularly to a connection structure in a branching connector in a high-pressure fuel rail serving to pass a fuel under a pressure exceeding 1,000 kgf/cm.sup.2 to an internal combustion diesel engine.
2. Description of the Prior Arts
FIG. 10 shows a conventional type of connection structure for a branching connector such as a branch pipe in a manifold serving as a high-pressure fuel rail, wherein a branch pipe (13) is inserted in a straight hole (12) formed in a high-pressure fuel main pipe (11) perpendicularly to the axis of the pipe and welded together in the joined state.
In the connection structure of this nature, however, the welded portions (14) are liable to be embrittled possibly to the extent of entailing the phenomenon of of fuel scatter or the separation of the branch pipe (13) in some cases because the welded portions by nature are exposed to repeated application of an ultra-high fluid pressure frequently exceeding 1,000 kgf/cm.sup.2 and to incessant exertion of vibrations generated by the engine.
In place of said connection structure and in order to resolve the problem involved therein, a connection structure in which branch pipes are mechanically connected to a main pipe by means of a concavo-convex fitting was proposed by the present application in the U.S. Pat. No. 4946205.
In the proposed connection structure as illustrated in FIG. 11, a connection head portion (18) shaped in the form of a truncated cone on the connection terminal of a branch pipe (17) is pressed via a bowl-like sealing member (19) into tight contact with the pressure receiving bearing surface being an inner peripheral surface of a branch hole (15) formed in the shape of an inverted cone in a main pipe (11), said connection head portion being fastened with a nut (20).
In the connection structure of such a concavo-convex system, the sealing effect is much greater than the connection structure shown in FIG. 10, but as illustrated in FIG. 12, as the nut (20) is increasingly tightened, the bowl-like sealing member (19) is penetrated by the outer peripheral edge (21) of the pressure receiving bearing surface and possibly deformed by tension from the connecting head portion (18), thus causing clearance between the bearing surface and the sealing member. And as illustrated in FIG. 13, when the connection head portion (18) is caused to tilt or move eccentrically, one end of the portion may be penetrated by the outer peripheral edge (21) to cause deformation, while the other end may be lifted from the branch hole (16) to cause clearance, thus making it impossible to obtain the desired surface pressure despite increased tightening torque produced by the nut (20). This is because the tightening torque generated by the nut 20 does not normally work as thrust force on account of the bite by the outer peripheral edge (21) into the connection head portion (18) on one side.
In FIGS. 12 and 13, if clearance is produced between the sealing member (19) and the pressure receiving bearing surface or between the connection head portion (18) and the bearing surface, the fuel inside may spatter through the gap or the branch pipe (17) may be separated.